The present invention relates to data recording devices for recording and reproducing data on optical disks such as CD-R (Compact Disc Recordable) or CD-RW (Compact Disc Rewritable).
When recording data in optical disks such as CD-Rs and CD-RWs, an entire track or optical disk needs to be completed with one recording operation, as implied by the names of methods for writing disks, such as Disk-at-once and Track-at-once. Thus, if a data recording fails, the whole optical disk becomes unusable or the previously recorded data are lost. The recording failure can be caused by, for example, a buffer underrun error. The buffer underrun error occurs because the buffer, in which recording data are temporarily stored, is emptied when the data transfer speed of the recording data transferred from the host is slower than the data recording speed of the optical disk device and consequently a recording operation cannot be continued.
In view of this problem, Japanese Unexamined Patent Publication Nos. 10-49990 and 2000-40302 disclose an apparatus that can temporarily suspend recording operation when the recording failure is expected to occur and can restart afterwards. This apparatus has a configuration as follows. When the recording data held in the buffer reduces while the recording operation is being underway, that is, when a buffer underrun error is likely to occur, the recording operation is interrupted, and the internal information at that point is held, specifically, such as the data to be recorded next (more specifically, the pattern data indicating a pit pattern to be actually recorded and the data which are necessary to generate the pattern data) and the information indicating that the recording should be restarted at what clock of which frame. When a predetermined amount of data has been accumulated in the buffer, and after a subcode sync is detected, the recording location for the next data is detected by counting the PLL (Phase Locked Loop) clock of the channel bit, and then the recording is restarted.
However, the above-described device, which detects a recording location by counting the PLL clock, has at least the following problem. When the data that are up to the recording interruption can be properly reproduced, the above-described device can restart recording at comparatively high accuracy so that continuous data can be recorded with few or no seams (overlaps and gaps). However, when errors are caused when reproducing the recorded data, for example, when the optical disk is damaged by a scratch or when the pit pattern is unstable during the recording due to external vibration or the like, the device cannot restart from an appropriate recording location. Optical disks are susceptible to damage, and they often cause recording and/or reproducing errors due to scratches or the like. During a normal reproducing operation, such errors are in many cases recoverable and the data reproducing can be properly performed with the use of a predetermined error correction process. In cases where the interrupted recording is to be restarted, however, if the synchronization of PLL is disrupted and the phase of the PLL clock is shifted at a location where a reproducing error occurs, the location at which the data have been last recorded before the interruption of the recording cannot be accurately detected, and as a result, the location of restart of the recording is displaced. Consequently, a seamless and continuous recording cannot be attained.